At present, there are known various printing methods used to print characters, images, information, and the like on printing media. An inkjet printing method has widely been used in printing apparatuses, copying machines, and the like because of low noise, low apparatus cost, low running cost, and compact apparatus can be facilitated.
A conventional serial inkjet printing apparatus prints one page by alternately repeating main scanning by a printhead and sub-scanning of conveying a printing medium. A memory having a memory capacity enough to store all data to be printed by one main scanning at a main scanning printing width printable by a printing apparatus is used as a print buffer for storing data to be printed by the printhead. After all data to be printed by one main scanning are stored in the print buffer, main scanning of the printhead starts to perform printing.
Recently, in order to achieve color printing, higher image quality, higher resolution, and higher-speed printing, the number of printheads and the number of printing elements (ink discharge elements) arranged in each printhead tend to increase.
A larger number of printheads and a larger number of printing elements arranged in each printhead increase the data amount printed by one main scanning. The memory capacity necessary for the print buffer increases, resulting in a high apparatus cost.
To prevent this, Japanese Patent Laid-Open No. 58-146929 discloses a technique of managing an address at which print data is stored, efficiently using a memory, and performing printing with a memory capacity smaller than a data amount printed by one main scanning.
This reference, however, does not disclose processing of null data as data representing no printing. The use of the memory is not optimally efficient. Also, this reference does not disclose printing operation when data transfer to the memory does not catch up with printing operation.
Japanese Patent Laid-Open No. 11-259248, which corresponding to U.S. Pat. No. 6,097,499 discloses a technique of starting main scanning before the completion of receiving data of one main scanning.
The technique disclosed in this reference assumes that print data is received before actual printing by main scanning. A host apparatus such as a computer which transfers print data to a printing apparatus must continuously execute printing without any interrupt or interference of data transfer.
Windows System® which is widely used as the OS of recent computers is a general-purpose multitask system. In practice, the computer hardly performs only data transfer during printing. The program of a printer driver installed in a computer allows continuously executing printing without any interrupt or interference of data transfer. In this case, the merit of the multitask system is lost. This reference does not disclose processing of null data as data representing no printing. The use of the memory is not optimally efficient.
These problems are not unique to an inkjet printing apparatus but common to all serial printing apparatuses.